Liquid crystal displays to which electrostatic fields are applied in parallel to the substrate are known as a lateral electrostatic field method or an IPS (in-plane switching mode). U.S. Pat. No. 6,762,814 and Japanese laid-open patent application publication No. 9-80424 disclose such systems using teeth electrodes. In this system, liquid crystal molecules mainly rotate within a plane in parallel to a substrate, so that it is well known that a change in a double refraction rate is small between application and non-application of electrostatic fields.
However, in the IPS mode, though the variation in the birefringence of the liquid crystal itself is low, it is known that light leaks when viewed at an oblique angle deviating from an absorbing axis of a polarizing plate due to a characteristic of the polarizing plate. To reduce the light leakage in the inclined viewing direction, a system using a retardation compensation plate is disclosed in Japanese laid-open patent application publication No. 2001-350022. However, this document discloses improvement of viewing angles only in the polarizing plates, the document considers the effect of liquid crystal in a VA (Vertically Aligned) mode, but does not discloses compensating the effect of the liquid crystal layer in the IPS mode. Further, the polarizing plate generally uses plates made of TAC (triacetylcellulose) on both sides of the polarizing layer for supporting. However, this document does not disclose retardation compensation in consideration of behavior of the liquid crystal layer due to a retardation difference in the thickness direction of the supporting plates.
Further, Japanese patent No. 3204182 discloses means for resolving a problem that color shift at white portions occurring in accordance with a viewing direction. However, it does not disclose improvement in a displaying characteristic of black representation.
Further, Japanese patent No. 2982869 discloses a structure in which a retardation compensation plate is arranged on an inside of only one polarizing plate to improve a viewing angle characteristic of the black representation. This system considers the effect of the supporting palates of TAC arranged on the both sides of the polarizing plate. However, our study shows that retardation compensation with only one retardation compensation plate cannot provide sufficient decrease in luminance at black-representation condition at an inclined viewing angle as well as cannot reduce the color shift due to wavelength dispersion in the liquid crystal layer. Further, this document does not disclose a difference in the retardation compensation depending on whether the alignment axis (slow axis) of the liquid crystal molecules at the black-representation condition is in parallel or perpendicular to an absorbing axis of the polarizing plate on an incident side, which is a feature of the present invention. This document only discloses, in embodiments, a structure in which the alignment axis of liquid crystal molecules is perpendicular to the absorbing axis of the polarizing plate on the incident side. Further, our study shows there is a problem in the conventional retardation compensation system using only one retardation compensation plate on one side of polarizing plate, so that the color shift occurs in accordance with a viewing orientation.
Further, Japanese laid-open patent application publication No. 2001-290149 discloses thicknesses of RGB color filters and a retardation compensation film.